Bouillie Bordelaise: the Médocain fungicide which is kind of blue

Pictured above is a familiar sight in garden centres and DIY stores throughout France: rows of packs of powder used to produce the best-selling fungicide Bouillie Bordelaise, or “Bordeaux Mixture”. As my knowledge of Bouillie Bordelaise was very slim (I knew that it was blue, but that was about all), I decided to investigate!

First things first, what is Bouillie Bordelaise? As so often, Wikipedia was my first port of call: the introductory paragraph states that the fungicide is “a mixture of copper (II) sulfate (CuSO4) and slaked lime (Ca(OH)2) used in vineyards, fruit-farms and gardens to prevent infestations of downy mildew, powdery mildew and other fungi”. The “preventative” aspect is important as the Wikipedia entry adds that “its mode of action is ineffective after a fungus has become established”. In other words, you have to treat the plants before they fall sick.

That is all very well and interesting, but what is the connection with Bordeaux? To find out we need to rewind to the late 19th century and the many outbreaks of vine diseases throughout France caused by pests carried on vines brought to Europe as botanical specimens of American origin: vineyards had to fight back against pests such as Phylloxera vastatrix, but also mildew and other diseases caused by fungi.

Scientists began looking seriously into the matter. One of the most prominent was the ampelographer (vine expert) and botanist Alexis Millardet (1838-1902), a Bordeaux university professor who, in 1882, was out and about in the Médoc wine-growing area when he noticed some distinctly healthy-looking vines in Saint-Julien-Beychevelle, on the grounds of Château Ducru-Beaucaillou. Stopping to enquire, the person who oversaw the land, one Ernest David, explained that Médoc vine-owners had developed the practice of spraying a mixture of copper sulfate and slaked lime on roadside vines to dissuade passers-by from helping themselves to grapes. It got Millardet thinking about the potentially protective properties of the solution.

The vines and grounds of Château Ducru-Beaucaillou, where the Bouillie Bordelaise story began.

With the help of a fellow researcher, the Chemistry professor Ulysse Gayon, Millardet conducted experiments on a number of home-grown vines. Initial results were encouraging and the scientists were given the go-ahead to roll out large-scale trials on the vines back at Ducru-Beaucaillou and further south at Château Dauzac in Labarde, which belonged to the same landlord, Nathaniel Johnston, and was also run by Ernest David. The trials, which ran from 1883 to 1885, led to the local eradication of mildew by 1886 (similar breakthroughs were also achieved by other people in Bourgogne region of France at the time), and enabled the men to gradually perfect the mixture which would come to be known as Bouillie Bordelaise, the formula of which has evolved little over the ensuing 130 years.

That recipe remains in the public domain and is as follows (based on the information found here), if you’d like to produce 10 litres of the stuff from scratch rather than purchasing an off-the-shelf pack of readymade powder. First, be sure to stock up on the following equipment and ingredients: a pair of sturdy gloves, one 10-litre bucket, one 15-litre plastic bucket, 300g of slaked lime, 200g of copper sulphate and 10 litres of water.

Step 1: put on those sturdy workgloves.

Step 2: using the 10-litre bucket, dissolve 300g of slaked lime in 6 litres of water and stir the mixture with a stick to produce lime slurry.

Of course, given the chemistry at work here, handling Bouillie Bordelaise is not without risk. It can cause general skin complaints (hence the gloves) or conjunctivitis if it enters into contact with the user’s eyes. The issues don’t stop there as even mild ingestion of the product can lead to nasal irritation and respiratory problems. The fungicide has also been identified as having triggered a deadly occupational disease among Portuguese vineyard workers: "Vineyard sprayer's lung". According to www.ncbi.nlm.nih.gov, “the radiographic picture resembles that of silicosis with micronodular disease in the early stages and progressive massive fibrosis in later stages, eventually resulting in endstage lung disease. The patients have a downhill course due to respiratory failure.” Don’t say I didn’t warn you.

A Ducru-Beaucaillou vine leaf.

In the meantime, Bouillie Bordelaise continues to be a staple product stored in the sheds of amateur and professional gardeners alike. Back in the Médoc wine-growing area, when inspecting the vines at Château Ducru-Beaucaillou, where the Bordeaux Mixture story really took shape all those years ago, I spotted traces of a white-coloured fungicide on some leaves – whether this was the “colourless” variant of Bouillie Bordelaise was unclear, but whatever the product used, the vines still appeared to be in rude health.